Method of continuous casting of steel using an oscillating mold

ABSTRACT

A method for continuous casting of steel with oscillating mold is disclosed according to which maximum mold oscillation speed, ingot withdrawal speed, oscillating frequency and displacement stroke for vertical mold oscillations are interrelated to permit welding of cracks in the ingot skin within periods of less than half a second per down stroke of the mold.

United States Patent Vogt et a1. H lMarch 20, 1973 METHOD OF CONTINUOUS CASTING [56] References Cited OF STEEL USING AN OSCILLATING UNITED STATES PATENTS MOLD 2,135,183 11/1938 Junghans ..164/83 [75] Inventors: Gerd Vogt, Strump; Klaus Wunnen- 2,815,551 12/1957 Hessenberg et a1. 164/83 berg Duisburg; Joachim 3,118,195 1/1964 Gouzou et a1. ..l64/83 Ger-many FOREIGN PATENTS OR APPLICATIONS [73] Assignee Mannesmm Akfiengmuschaf" 535,188 7/1955 Belgium ..164/82 Dusseldorf. Germany 783,517 1 9/1957 Great Britain..... [22] Filed: Jan. 11 1971 909,464 10/1962 Great Bntaln ..164/83 [21] Appl. No.: 105,240 Primary Examiner-R. Spencer Annear Attorney-Smyth, Roston & Pavitt [30] Foreign Application Priority Data [57] ABSTRACT Jan. 14, 1970 Germany ..P 20 02 366.9 A method for continuous casting of teel oscillating mold is disclosed according to which maximum [52] US. Cl ..l64/83, 164/260 mold oscillation speed, ingot withdrawal speed, oscil- [51] Int. Cl. ..B22d 11/02 lating frequency and sp a nt str r v rt al 53 Fi of Search 1 4 2 3 270 27 R, 0 mold oscillations are interrelated to permit welding of cracks in the ingot skin within periods of less than half a second per down stroke of the mold.

1 Claim, 1 Drawing Figure 1 1 503a,- iii nu T ,1 I 1 V; l 'I 7 i 2 v [mm "1 i 1 0 v i..- 1 .5555 $1,155 575 1 V 0 0! ll 1.5 20 2.! l0 .1) .0

METHOD OF CONTINUOUS CASTING OF STEEL USING AN OSCILLATING MOLD The present invention relates to a method for continuous casting of steel using a mold that undergoes oscillatory, sinusoidal movement in dependence upon the speed of withdrawing the ingot.

The solidified skin of developing cast ingot tends to adhere to the wall of the mold during withdrawal. In order to avoid such sticking, it is known to impart an oscillatory motion upon the mold. Among the possible varieties of motion, sinusoidal oscillation is almost exclusively used today. The oscillatory motion has up and down components and the instantaneous speed of the mold, when moving down, is made to temporarily exceed the ingots withdrawal speed. Note that the withdrawal speed of the ingot is not referenced to the mold exit but to a stationary reference.

As a consequence of these mold oscillations, the solidified shell or skin of the ingot (the ingot being still predominantly liquidous in its interior at that point), is alternately subjected to compression and tension forces. During the down stroke of the mold, there is compression of the skin, particularly as the mold passes the ingot. The compression provides welding action for closing any cracks or fissures that may have formed in the skin. This period of compression, when the mold moves down faster than the ingot, is usually maintained constant and within the range of 0.5 to 1.0 seconds, as has been suggested in a paper published in STAL (German language issue); l967, Vol. 10, pages 955 to 958.'

In accordance with that publication, periods shorter than 0.5 seconds are insufficient for such inherent welding of any cracks in the shell. Under such conditions, the withdrawal speed is limited, otherwise the mold oscillations would be too vigorous, i.e., too fast at too large an amplitude.

The problem solved by the present invention is to find a mode of operation that permits (a) rather high withdrawal speeds of the ingot at (b) periods of skin compression (when the mold velocity exceeds the withdrawal speed during a downstroke) shorter than the heretofore deemed limit of half a second.

In accordance with the invention, it is suggested to combine the following parameters for mold oscillation. The ratio of mold peak velocity-to-ingot withdrawal speed is to be within the range of about 1.4 to about 2.2. The mold oscillation frequency should be about 40 to about 80 min for a compression period to remain between 0.2 to 0.4 seconds. The ingot speed should be above 1.2 meter/minute and the displacement of the mold is selected to be proportional to the ingot withdrawal speed on basis of the said ratio and compression period as parameters in the proportionality relation. These parameters are to be constant during operation.

Upon using the method, i.e., upon operating a mold at parameters in the stated ranges, ingots were produced at high withdrawal speeds and excellent surface conditions. Cracks of the type stated where not observed. The result was surprising indeed as the compression period was well below the half-a-second period heretofore regarded as lower limit. As the com- I pression and welding period within each mold oscillating cycle is quite short, displacement is accordingly small.

While the specification concludes with'claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, feature and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

The FIGURE is a graph showing operating characteristics for an oscillating mold with ingot withdrawal speed plotted against maximum mold displacement, and oscillating frequency as parameter.

Proceeding to the detailed description of the drawing, the family of curves as plotted in the graph have been arrived at as follows. The instantaneous displacement of the oscillating mold can be expressed mathematically by the equation D=A-cos (wt)=H/2-coswt (1) Through differentiation we obtain the velocity of the mold V =A-w-sin (wt) 2 In these equations, A W =V denotes the peak velocity of the mold. A is the amplitude of the oscillatory displacement of the mold, while 2 A J is the maximum displacement, i.e., the distance between the points of reversal of the mold during oscillation. t denotes time and is given in minutes in the graph. W= 2 1:" n, wherein n is the frequency of the oscillatory motion.

During each downstroke half cycle of the oscillating mold, the mold has temporarily speed equal to or in excess of the ingot withdrawal speed Vg. The period time (compression period) where Vk Vg is derived as follows:

The mold velocity equals the ingot withdrawal speed twice in each cycle and the period between is the compression period t for the solidified skin of the ingot in the mold. These two points in time are given as follows:

In this relation denotes the ratio of peak. mold velocity V to ingot withdrawal speed Vg. f (7) denotes the expression in parenthesis and indicates to be only a function of that ratio 7.

Equation (3) teaches that the compression period is defined by that ratio 7 and by the oscillation frequency. Restating the relation,

teaches that upon selection of y and of a compression' period At the frequency for the mold oscillation is selected therewith. As stated, this period At is available for welding any cracks as compression is imparted upon the skin of the ingot.

In accordance with a first feature of the invention, the ratio 7 of maximum mold speed to ingot withdrawal speed is to be selected to fall in the range from about 1.4 toabout 2.2. The moldoscillation frequencynis to be selected so that the compression period At is to be about 0.2 to 0.4 seconds. This requires the oscillation frequency n to be in the range from about 40 to above 80 min.

On basis of the relationship l) and (2) above, we obtain km n H combining (6) with chosen as one parameter for the particular family ofcurves plotted, with three different oscillation frequencies and compression periods At for crack welding as variable parameter.

In particular, the proportionality relation is within the range from H 6 Vg to about H 12 Vg, the proportionality factors being mm per meter per minute, H given in millimeters, withdrawal speed in meter per minute accordingly.

Having chosen the parameters y and n to obtain a compression period At within the given range, one of the characteristics can be plotted. The withdrawal speed Vg (and therefor the oscillation speed on basis of the chosen ratio can then be chosen to be rather high, and the needed displacement H is then controlled in dependence upon ingot withdrawal speed along the selected characteristics as taken from the graph.

For a different ration 7, a different family of curves can be plotted, for a chosen compression period of frequency one of the curves of the family is selected. For values of 'y in the range of about 1.4 to about 2.2 the performance is excellent. For a 'y 1.2, the resulting displacement H is rather large, and it was found that the surface of the ingot will be rather rough under such circumstances. Also, too large a displacement is not desirable from standpoint of equipment operation. A ratio 'y of 2.4 also was found to lead to too large a displacement, and therefore is not desirable. Thus, the range for 'y from about 1.4 to about 2.2 was found to yield the most satisfactory results.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

We claim:

1. The method for continuously casting steel using an sinusoidally oscillating mold, comprising the steps of:

withdrawing the ingot at a speed in excess of 1.2 meter/minute; providing the sinusoidal oscillations at a maximum mold oscillation speed so that, as a first parameter, the ratio of maximum mold oscillation speed and ingot withdrawal speed falls within the range of about 1.4 to 2.2; and

oscillating the mold at a frequency as a second parameter from within the range of about 40 to about cycles min, so that the period within each oscillation period in which the mold speed exceeds the ingot speed is about 0.2 to 0.4 seconds and the displacement for the mold is proportionate to the mgo withdrawal speed, on basis of the first and second parameters. 

1. The method for continuously casting steel using an sinusoidally oscillating mold, comprising the steps of: withdrawing the ingot at a speed in excess of 1.2 meter/minute; providing the sinusoidal oscillations at a maximum mold oscillation speed so that, as a first parameter, the ratio of maximum mold oscillation speed and ingot withdrawal speed falls within the range of about 1.4 to 2.2; and oscillating the mold at a frequency as a second parameter from within the range of about 40 to about 80 cycles min 1, so that the period within each oscillation period in which the mold speed exceeds the ingot speed is about 0.2 to 0.4 seconds and the displacement for the mold is proportionate to the ingot withdrawal speed, on basis of the first and second parameters. 